Prior art references considered to be relevant as a background to the invention are listed below. Acknowledgement of the references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the invention disclosed herein. U.S. Pat. No. 4,945,647 discloses a gyrocompassing system intended for land based equipment requiring north reference information, and includes a novel gyrocompass implementation which enables utilization of high grade inertial sensors while achieving the desired goal of moderate cost. The north finding system is designed to provide high accuracy with fast reaction time over a wide temperature range without the aid of heaters and other auxilliary equipment. The arrangement is specifically configured to tolerate settling and/or oscillatory base motion without additional reaction time or degradation of gyrocompassing accuracy.
U.S. Pat. No. 5,060,392 discloses a gyrocompassing system intended for land based equipment requiring north reference information, and includes a novel gyrocompass implementation which enables utilization of high grade inertial sensors while achieving the desired goal of moderate cost. The north finding system is designed to provide high accuracy with fast reaction time over a wide temperature range without the aid of heaters and other auxiliary equipment. The arrangement is specifically configured to tolerate settling and/or oscillatory base motion without additional reaction time or degradation of gyrocompassing accuracy. The input axis of a gyroscope used in the system is skewed, so it can measure a component of gimbal rotation, thereby eliminating the need for independently measuring the relative gimbal angle. Absolute position alignment between the gimbal and the system case as is required, is accomplished by an appropriate stop arrangement, which is an easier task than measuring the relative gimbal angle as aforenoted.
U.S. Pat. No. 5,272,922 discloses a vibrating element angular rate sensor system and north seeking gyroscope. An angular rate sensor system preferably comprising closely spaced vibrating drive and sensing elements in a paired tuning fork configuration mounted to rotate about a rotational axis oriented perpendicular to the sensitive axes. The rotational drive assembly includes an encoder to modulate sensing element orientation, and coupling means to transmit drive and output signals to and from the rotating elements. Each pair of sense and drive elements are disposed in non-aligned parallel side-by-side opposition across the axis of rotation. The elements may be carried on torsional masses including a resilient coupling therebetween. The angular rate sensor system may be utilized as a north-seeking gyroscope in applications such as mining, surveying, or artillery. The phase of the sinusoidal sensor output signal corresponds to the orientation between the sensitive axis of the sensing elements and the earth's angular rate vector to produce a reference to geographic north. The electronic filter includes a signal generator, two phase-locked loops, AC amplifiers, bandpass filter, comparator, counter-divider, and latch to iterate a steady phase reading. A settling time of approximately 30-60 seconds is required to resolve a heading reference within +0.1.degree of geographic north. A two axis low bias embodiment of the angular rate sensor system may be utilized alone or in combination with a similar system to provide complete angular rate sensing along a desired common axis, or with a second stationary angular rate sensor to enhance the bandwidth and DC response of the stationary angular rate sensor.
U.S. Pat. No. 5,272,922 discloses a high resolution gyro system for precise angular measurement. The system includes for planar angular measurements a gyro—preferably a laser gyro—and an angle encoder mounted with their sensitive axes coaxially on a turntable shaft, which is rotatably mounted in a case and driven at constant speed with respect to the case. The angular rate should be high enough to operate the laser gyro above the lock-in rate. For spatial angular measurements and navigation three gyros are mounted with their sensitive axes spatially arranged with respect to the turntable shaft to sense the same component of its angular rate. For averaging errors due to gyro scalefactor and drift, the turntable is mounted on a second shaft with its axis perpendicular to the turntable. The second shaft is provided with a second encoder and a motor rotating the second shaft. The processing of the signal readout of the gyro(s) and encoder(s) allows to increase the accuracy, resolution and bandwidth of angular measurements with respect to a locally fixed basis or to inertial space.
U.S. Pat. No. 5,703,293 discloses a rotational rate sensor with two acceleration sensors. A rotational sensor has a vibrating weight with two acceleration sensors mounted on it. The two acceleration sensors are designed to detect forces acting at a right angle to each other. The vibrating weight is set in vibration by means of driving devices, and rotation of the rotational sensor about two axes of rotation that are normal to each other is detected with the help of the acceleration sensors. The Coriolis forces in a plane are determined in this way.
U.S. Pat. No. 6,502,055 discloses a method and apparatus for determining the geographic heading of a body, and a method of determining an orientation of a body. The method includes the steps of measuring an acceleration of the body in a first direction, measuring an acceleration of the body in a second direction different from the first direction, the first direction and the second direction defining a plane, measuring an acceleration perpendicular to the plane in a coordinate system rotating about an axis perpendicular to the plane, and inferring the orientation of the body from the three measurements.
U.S. Pat. No. 6,621,460 discloses instrument alignment devices and methods for determining an instrument boresight heading. The apparatus comprises an instrument having a boresight, an elevation positioner for positioning the elevation of the instrument boresight having an elevation axis, an azimuth positioner for positioning the azimuth of the instrument boresight having an azimuth axis and a sensor including a gyro having a sensitive axis. The method comprises recording a first output of a gyro of an azimuth positioner having an instrument boresight azimuth heading in a first position, rotating the azimuth positioner to a second position, recording a second output of the gyro and rotating the azimuth positioner to a third position, recording a third output of the gyro and determining the azimuth heading relative to true north from the first, second and third output.
U.S. Pat. No. 7,412,775 discloses a gyroscope north seeker system and method which includes a sensor system and method for determining a relative direction to true north. The system comprises at least one angular rate sensor, such as a MEMS sensor, which has an input axis and a rotation axis. The sensor comprises a motor drive structure, a motor signal output from the motor drive structure, a gyroscope, and a sensor rate output from the gyroscope for a sensor rate signal. A frequency divider is in operative communication with the motor signal output, and a spinning device is coupled to the angular rate sensor. A spinning device motor is coupled to the spinning device and is in operative communication with the frequency divider. The spinning device motor has an axis of rotation that is substantially perpendicular to the input axis of the sensor. The spinning device motor is configured to be driven by a periodic signal from the sensor. A position of the spinning device is synchronized to the periodic signal to generate a spinning device position signal. A phase detector is in operative communication with the spinning device motor and with the sensor rate output. The relative direction to true north is determined from a phase differential between the spinning device position signal and the sensor rate signal.
There is a need in the art to provide for a new technique for North finding incorporated in a payload.